1. Field of the Invention
The present invention relates to an apparatus for plasma processing a semiconductor substrate by using microwaves.
2. Description of the Related Art
Japanese Laid-Open Patent Publication No. 2002-299331 discloses an apparatus for plasma processing a semiconductor substrate by using microwaves. The plasma processing apparatus includes a chamber, and a susceptor holding a substrate to be processed is provided in the chamber. A shower plate is arranged in the chamber at a position corresponding to the substrate placed on the susceptor. The shower plate includes a dielectric window main body formed of a low loss dielectric such as alumina and having a plate shape in which a plurality of opening portions for spurting plasma gas are formed, and a dielectric cover plate formed of the low loss dielectric and arranged above the dielectric window main body.
The shower plate spurts plasma excitation gas such as Ar or Kr that is externally supplied at a constant concentration into a space in the chamber from the opening portions. Additionally a radial line slot antenna is placed in the chamber above the dielectric cover plate. Microwaves from an external microwave source are radiated into the chamber through the radial line slot antenna to excite the plasma excitation gas spurted into the space of the chamber. A gap between the dielectric cover plate and a radiation surface of the radial line slot antenna is maintained at atmospheric pressure.
By using the radial line slot antenna, a uniform high density plasma is generated in a space directly under the dielectric window main body. The high density plasma generated in this manner has a low electron temperature so that damage to the substrate may be prevented. Also, metal contamination due to sputtering of an inner wall of the chamber may be prevented. Furthermore, since the generated plasma has high density, a substrate process such as film forming can be efficiently carried out at high speed.
With an increase in the size of the substrate, the size of the plasma process apparatus has increased too. Also, the size of the shower plate including the dielectric window main body and the dielectric cover plate has increased. The shower plate is formed of a dielectric such as Al2O3, AlN, or SiO2. Since the inside of the plasma processing apparatus is maintained at a reduced pressure, a force in a downward direction perpendicular to the shower plate is generated and applied to the shower plate having a large area. In this state, when an external shock or thermal shock is applied to the shower plate, the shower plate may be easily broken.
When the shower plate is broken, although the dielectric window main body is covered with the dielectric cover plate, the plasma excitation gas in a process container and the process gas or film forming gas supplied to the inside of the chamber are leaked out through a gap between the dielectric cover plate and the radiation surface side of the radial line slot antenna, because there is the gap between the dielectric cover plate and the inner wall of the chamber. Since the gap between the dielectric cover plate and the radiation surface of the radial line slot antenna is in communication with air in the atmosphere, the gas in the process container may be leaked out of the plasma process container.
In particular, since the pressure of the plasma excitation gas supplied to the shower plate is several hundreds torrs high, the amount of the gas leaking when the shower plate is broken is very large. Also, since the film forming gas or cleaning gas is very toxic, it is very dangerous when the shower plate is broken and thus the toxic gas is leaked out of the apparatus.